1. Field of the Invention
The present invention relates to a biochip, and more particularly, to a biochip having an image sensor with a back side illumination photodiode structure which collects light from the back side of a wafer in order to improve capability of sensing light emitted from reaction regions of a biochip.
2. Description of the Related Art
In general, a biochip is manufactured in a type in which reference samples constituted biological molecules such as DNAs, proteins and the likes are regularly arranged on a substrate made of a material such as glass, silicon and nylon.
Biochips are divided into a DNA chip, a protein chip, and so forth, depending upon the kind of reference samples to be arranged. Basically, a biochip uses biochemical reactions between reference samples and target samples which are fixed with respect to a substrate. Representative examples of the biochemical reactions between the reference samples and the target samples include a complementary binding of DNA bases and an antigen-antibody reaction.
For the most part, diagnosis by a biochip is implemented by detecting a degree to which a biochemical reaction occurs, through an optical procedure using an image sensor. The optical procedure generally uses a fluorescence or luminescence phenomenon.
FIG. 1 is a view illustrating the configuration of a conventional biochip having an image sensor with a front side illumination photodiode structure.
Referring to FIG. 1, a conventional biochip 100 having an image sensor with a front side illumination photodiode structure includes a biochip layer 100a and an image sensor layer 100b. 
The biochip layer 100a has a plurality of first reaction region 110a, second reaction region 110b and third reaction region 110c which have shapes of grooves. The first, second and third reaction regions 110a, 110b and 110c respectively have target samples 111a, 111b and 111c in the upper portions thereof and reference samples 112a, 112b and 112c in the lower portions thereof.
The image sensor layer 110b has a plurality of first front side illumination photodiode 151a (PD1), second front side illumination photodiode 151b (PD2) and third front side illumination photodiode 151c (PD3) which are formed in an epitaxial layer 150 of a wafer.
A plurality of stacked metal wiring lines 131 and 133 are formed in an interlayer dielectric 130 which is formed on the upper surface of the epitaxial layer 150.
However, in the conventional biochip 100 having an image sensor with a front side illumination photodiode structure, light 120, which is emitted depending upon degrees of biochemical reactions between the target samples 111a, 111b and 111c and the reference samples 112a, 112b and 112c of the plurality of first, second and third reaction regions 110a, 110b and 110c, is likely to be absorbed by the metal wiring lines 131 and 132 which are formed over the plurality of first, second and third front side illumination photodiodes 151a, 151b and 151c, as a result of which the light sensitivity of the plurality of first, second and third front side illumination photodiodes 151a, 151b and 151c may be degraded.
Meanwhile, in the manufacture of the biochip layer, a surface treatment technology is regarded important for the attachment of bio-materials. That is to say, in order to allow the bio-materials to be easily attached to a substrate, surface treatment is performed in such a way as to provide hydrophilicity or hydrophobicity. Such surface treatment is performed mainly using plasma.
In the conventional structure adopting the front side illumination (FSI), as the plasma is incident on the photodiodes during the surface treatment, the dark current of the photodiodes may be increased. Further, due to the fact that the biochip layer is formed on the interlayer dielectric, solutions, which are employed in the manufacture and reaction procedures of the biochip layer, may infiltrate into underlying circuits by passing through the interlayer dielectric. As a consequence, problems may be caused in that it is difficult to form the interlayer dielectric and limitations may exist in performing the surface treatment for the biochip layer and using reacting solutions, etc.